1. Field of the Invention
The present invention relates to a band brake with evenly distributed braking force application and a transmission using such a band brake. In at least one embodiment, evenly distributed braking force is applied directly to a rotating element.
2. Background and Description of the Related Art
Epicyclic gear sets including a sun gear, planet or pinion gears, a planetary carrier, and a ring gear, are commonly used in automatic automotive transmissions. Automotive automatic transmissions generally contain several epicyclic gear sets. Gear ratio selection involves holding some elements of the epicyclic gear sets motionless while allowing the other elements of the epicyclic gear sets to rotate relative to the transmission case or housing. The elements of the epicyclic gear sets are selectively held motionless by the use of band brakes. These band brakes usually frictionally engage the ring gear directly, or the sun gear and the planetary carrier through a driving shell fixedly attached to the particular element, and hold the particular element of the epicyclic gear set motionless when drawn tightly around either the ring gear itself or a driving shell in the case of the sun gear and the planetary carrier. Each band brake is usually dedicated to the control of a respective element of a particular epicyclic gear set. The gear selection mechanism determines which band brakes are engaged and which band brakes are disengaged at any given time.
Each band brake is engaged by an actuating mechanism which draws the ends of the band brake together to thereby tightly draw the band brake around its respective ring gear or driving shell. The frictional force applied by the band brake is directly related to the force applied between the ends of the band brake by the actuating mechanism. This arrangement puts a great demand upon the actuating mechanism to supply sufficient braking force to hold the ring gear or driving shell motionless.
Depending upon the load under which the transmission is operating, the actuating mechanism may not be capable of providing adequate braking force. Further, conventional actuating mechanisms are prone to wear and failure. In addition, it would also be desirable to reduce the bulk of the conventional actuating mechanisms as much as possible. Therefore the need persists in the art for a means to amplify the force applied to a band brake by the band brake actuating mechanism. Also, it would be desirable to evenly distribute the braking force applied by the band brake so as to avoid lateral loads, i.e. loads directed transversely to the axis of rotation, which can damage the bearings supporting various rotating parts.
Overrunning clutches, one-way clutches, and torque limiters that apply a braking force to a rotating element are known in the art, but none are seen to involve the evenly distributed application of force to a band brake. The following are some examples of overrunning clutches, roller clutches, and torque limiters that have been proposed in the art.
U.S. Pat. No. 5,740,893, issued to Ken Yamamoto on Apr. 21, 1998, shows a one-way clutch which uses ball bearings to frictionally immobilize the inner bearing race when torque is applied in a first direction, while allowing free rotation of the inner bearing race when torque is applied in a second opposite direction. A split ring which fits into a groove in the outer bearing race carries the cam surfaces which wedge the ball bearings into frictional engagement with the inner race.
U.S. Pat. No. 5,706,700, issued to Yoshito Takagi et al. on Jan. 13, 1998, shows an overrunning clutch for starter motors. The clutch of Takagi et al. uses spring-biased rollers to immobilize the internally toothed ring gear of a planetary gear set when torque is applied to the ring gear in one direction, while allowing the ring gear to rotate freely when torque is being applied in the opposite direction.
U.S. Pat. No. 5,672,110, issued to Masahiro Kurita et al. on Sep. 30, 1997, shows a torque limiter that allows a driving shaft to disengage from a driven element when the torque load on the driven element exceeds a safe limit. The torque limiter of Kurita et al. uses a set of rollers that provide the frictional engagement between the driving shaft and the driven member. The rollers bear against an octagonal surface in the driven member and move into the corner recesses of the octagonal bearing surface if the load on the driven member exceeds a predetermined threshold.
U.S. Pat. No. 5,520,268, issued to Wenhua Li et al. on May 28, 1996, shows an overrunning clutch which uses a chain of triangular wedges to frictionally engage a shaft coupling when torque is applied in a first direction, while allowing free rotation of the shaft coupling when torque is applied in a second opposite direction.
U.S. Pat. No. 5,152,726, issued to Frederick E. Lederman on Oct. 6, 1992, shows a shiftable roller clutch that can replace the disk pack clutch in an automatic transmission. The rollers in the Lederman device are spring-biased and are held in a cage. The cage is shiftable relative to an outer bearing surface. With the cage in a first position, an inner rotating element can freewheel in both directions. With the cage in a second position, the inner rotating element can freewheel in one direction only in the same manner as an overrunning clutch.
U.S. Pat. No. 4,415,072, issued to Masao Shoji et al. on Nov. 15, 1983, shows a one-way clutch that uses spring-biased rollers between an inner and an outer race to prevent relative rotation between the inner and outer races in one direction while allowing relative rotation between the inner and outer races in the opposite direction.
U.S. Pat. No. 3,732,959, issued to Ernest U. Lang et al. on May 15, 1973, shows an overrunning clutch that uses a plurality of overlapping and interfitting clutch bands which engage a V-groove in an inner rotating member. The clutch bands are each individually anchored to an outer rotating member. Rotation of the inner member, relative to the outer member, in a first direction urges the clutch bands into frictional engagement with the V-groove, and the clutch bands are disengaged from the V-groove when the inner member is rotated, relative to the outer member, in a second direction which is opposite to the first direction.
U.S. Pat. No. 3,447,650, issued to Michel Dossier et al. on Jun. 3, 1969, shows a one-way friction coupling that uses brake shoes provided intermediate a rotating shaft and a sleeve. The shoes are cammed into frictional engagement with the sleeve when the shaft is rotated in a first direction relative to the sleeve, and the shoes are disengaged from the sleeve when the shaft is rotated, relative to the sleeve, in a second direction which is opposite to the first direction.
German Patent Number 925,489, issued to Aloys Zeppenfeld on Mar. 24, 1955, shows an overrunning clutch surrounded by a ring which is in frictional engagement with a brake band. With the brake band engaged, a shaft on which the overrunning clutch is mounted can rotate in only one direction. With the brake band disengaged, the shaft can rotate in both the clockwise and counter clockwise directions.
Italian Published Patent Application Number 487,591, by Terenzio Scalarini et al., dated Dec. 3, 1953, shows a selectively engageable roller clutch. When engaged, the roller clutch permits rotation in one direction only.
Soviet Inventors Certificate Number 1,810,662, dated Apr. 23, 1993, shows a roller clutch that allows rotation in one direction only.
None of the above inventions and patents, taken either singularly or in combination, is seen to describe the instant invention as claimed. In particular none of the above documents teach or suggest the evenly distributed application of force to a band brake.